1. Field of the Invention
The present invention relates, in general, to a metal-oxide-semiconductor field-effect-transistor (hereinafter "MOSFET"), which is generally employed in variety of semiconductor articles, and more particularly to an MOSFET having a nonuniform doping channel and a method for fabricating the same.
2. Description of the Prior Art
Hereinafter, description for a conventional lightly doped drain (hereinafter "LDD") MOSFET is to be, in brief, described for the better understanding of the invention with reference to FIG. 1, wherein reference numeral 1 designates a semiconductor substrate while reference numerals 2, 3, 4a; , 4b, 5a, 5b, 6, 7a, and 7b designate a channel, a gate oxide film, a high density source region, a high density drain region, a low density source region, a low density drain region, a gate electrode, a source electrode and a drain electrode, respectively.
A method for fabricating a submicron semiconductor device is required to maintain the high performance thereof as well as to secure the device reliability, scaling down the semiconductor device.
In particular, as this miniaturization proceeds toward nigher integration density, physical limits are generated. For example, device characteristics caused by the shortage of the thickness of the gate oxide film and the channel length, such as short channel effect, drain induced barrier lowering and punch through is deteriorated, so that the normal operation of the device cannot performed.
In order to unravel the above problems, an effort has been made such that the density of impurity ions for the channel is increased. However, this solution method causes the mobility of electron to be reduced, degenerating the transconductance (the ratio of the change of gate current to the change of gate voltage) of channel, the electric current characteristics and the device reliability.